1. Field of the Invention
This invention relates to an ignition system for use with an internal combustion engine, for example, an automobile engine, and also to an apparatus useful for such an ignition system.
2. Description of the Prior Art
In an ignition system used for igniting an internal combustion engine, for example, an automobile engine, a distributor having mechanical contacts has been incorporated for sequentially distributing a high voltage induced in an ignition coil to a plurality of spark plugs. However, this system has been encountered with, for example, the problem of noise generation due to incessant on-off of the distributor contacts and the problem of deterioration of the function of the distributor contacts due to wear, moisture, soiling and the like. This system has therefore been defective in that the noise generated from the distributor contacts provides a source of radio interference, and the useful service life of the system is shortened in addition to its reduced reliability.
With a view to obviate these defects resulting from the operation of the distributor having mechanical contacts, a so-called distributorless ignition system (which will be abbreviated as a DIS hereinafter) has been proposed.
Typically, the DIS comprises a plurality of series circuits each including a diode and a spark plug and connected in parallel to the secondary winding of an ignition coil such that the polarities of the diodes with respect to the secondary winding are inverted in every other one of the circuits so that the current flows through the circuits are alternately reversed and an electrical power source circuit connected to the primary winding of the ignition coil for supplying a primary current periodically in synchronism with the ignition timing of the internal combustion engine to be ignited through the DIS such that the polarity or direction of the primary current with respect to the primary winding is reversed every other cycle of the periodic supply thereby inducing into the secondary winding a high voltage periodically with a polarity inverted in every other cycle.
When the polarity of the high voltage induced in the secondary winding of the ignition coil coincides with the polarity of current turning on one of the diodes in the DIS having the arrangement above described, a spark generates across the spark gap of the spark plug connected in series with that diode, while when the polarity of the high voltage induced in the secondary winding of the ignition coil is opposite to that above described, the specific diode above described blocks the high voltage to prevent generation of a spark across the spark gap of the spark plug connected in series therewith. In this latter case, another diode conducts, and a spark generates across the spark gap of the spark plug connected in series therewith. Since the individual spark plugs are associated with the individual cylinders of the engine respectively, the spark energy necessary for igniting the engine can be sequentially supplied to the individual spark plugs by controlling the timing of supplying the primary current to the primary winding of the ignition coil.
Such a DIS is disclosed in, for example, U.S. Pat. No. 3,910,247 issued to G. Hartig on Oct. 7, 1975. Also, a more basic form of the DIS is disclosed in U.S. Pat. No. 1,335,933 issued to J. Bohli on Apr. 6, 1920. Reference to these U.S. patents will provide further detailed knowledge of the basic principle of the DIS.
The conventional DIS generally has no problem so long as the internal combustion engine incorporated with the DIS is under the normal operating condition, but it has been found that a problem arises sometimes when the engine is driven under an unusual operating condition such that the electrodes of some of the spark plugs are excessively worn or the circuit on the primary side of the ignition coil is energized in the state in which one or more of the spark plugs have been removed from the wiring on the secondary side of the ignition coil for the purpose of, for example, maintenance and inspection of the engine. In such an unusual operating condition, no spark ignition will occur in spite of induction of the high voltage across the secondary winding of the ignition coil. As a result, a surge voltage which is three to ten times as high as the secondary voltage appearing in the normal operating condition will be induced in the secondary winding of the ignition coil. This surge voltage is high enough to destroy the diodes when applied thereto in the reverse direction.